title: Metabolic Tumor Volume on PET Reduced More than Gross Tumor Volume on CT during Radiotherapy in Patients with Non-Small Cell Lung Cancer Treated with 3DCRT or SBRT.
abstract: OBJECTIVE
  We have previously demonstrated that tumor reduces in activity and size during the course of radiotherapy (RT) in a limited number of patients with non-small cell lung cancer (NSCLC). This study aimed to quantify the metabolic tumor volume (MTV) on PET and compare its changes with those of gross tumor volume (GTV) on CT during-RT for 3D conformal radiotherapy (3DCRT) and stereotactic body radiotherapy (SBRT).
  
  
  METHODS
  Patients with stage I-III NSCLC treated with a definitive course of RT ± chemotherapy were eligible for this prospective study. FDG-PET/CT scans were acquired within 2 weeks before RT (pre-RT) and at about two thirds of total dose during-RT. PET-MTVs were delineated using a method combining the tumor/aorta ratio autosegmentation and CT anatomy based manual editing. Data is presented as mean (95% confident interval).
  
  
  RESULTS
  The MTV delineation methodology was first confirmed to be highly reproducible by comparing volumes defined by different physicians and using different systems (coefficiency >0.98). Fifty patients with 88 primary and nodal lesions were evaluated. The mean ratios of MTV/GTV were 0.70(-0.07~1.47) and 0.33(-0.30~0.95) for pre-RT and during-RT, respectively. PET-MTV reduced by 70% (62-77%), while CT-GTV by 41% (33-49%) (p< 0.001) during-RT. MTV reduction was 72.9% and 15.4% for 3DCRT and SBRT, respectively (p< 0.001).
  
  
  CONCLUSIONS
  PET-MTV reduced more than CT-GTV during-RT, while patients treated with 3DCRT reduced more than SBRT. RTOG1106 is using during-RT PET-MTV to adapt radiation therapy in 3DCRT.
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, MI ; Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Thailand.
authors.forename: Pawinee
authors.initials: P
authors.lastname: Mahasittiwat
authors.forename: Shuanghu
authors.initials: S
authors.lastname: Yuan
authors.forename: Congying
authors.initials: C
authors.lastname: Xie
authors.forename: Timothy
authors.initials: T
authors.lastname: Ritter
authors.forename: Yue
authors.initials: Y
authors.lastname: Cao
authors.forename: Randall K
authors.initials: RK
authors.lastname: Ten Haken
authors.forename: Feng-Ming Spring
authors.initials: FM
authors.lastname: Kong
keywords: During Radiotherapy; GTV; Metabolic Tumor Volume; Non-Small Cell Lung Cancer